Centrifuge with intermittent sludge discharge

ABSTRACT

Sludge is discharged intermittently from the centrifugal rotor under control of a hydraulically actuated piston valve movable axially of the rotor. The piston valve has a radially inner area facing the rotor&#39;&#39;s separating chamber and partly defining a space within the rotor, and means are provided for maintaining this space free of liquid and thereby reducing the hydraulic pressure tending to shift the piston valve to its sludge-discharging position.

[ Jan. 15, 1974 CENTRIFUGE WITH INTERMITTENT SLUDGE DISCHARGE [75] Inventor: Klaus Hans Dieter Stroucken, Primary Examiner George H Krizmanich Ronnmge, Sweden Atl0rneyCyrus S. Hapgood Assignee:

Filed:

[73] Alfa-Laval AB, Tumba, Sweden July 7, 1972 Appl. No.: 2695845 1 eign Application Priority Data Sludge is discharged intermittently from the centrifu- Oct. 4, 197! gal rotor under control of a hydraulically actuated piston valve movable axially of the rotor. The piston Sweden.............................

valve has a radially inner area facing the rotors separating chamber and partly defining a space within the rotor, and means are provided for maintaining this space free of liquid and thereby reducing the hydraulic pressure tending to shift the piston valve to its sludge-discharging position.

[52] 233/20 A [51] Int. B04b 3/02 [58] Field of Search.............:.... 233/20 R, 20 A, 46,

3 Claims, 2 Drawing Figures 3,237,854 Thylefors 233/47 R 1 CENTRIFUGE WITH INTERMITTENT SLUDGE DISCHARGE The present invention relates to sludge centrifuges of the'type which operates with intermittent sludge discharge under control of an axially movable, hydraulically actuated piston valve.

Centrifuges of this type are disclosed, for example, in the published Swedish patent specification No. 336,561 and the published German Patent specification No. 2,041,372. The latter specification discloses a sludge centrifuge in which the piston valve has a radially inner area on its side facing the separating chamber of the centrifugal rotor and which is separated in liquid-tight fashion from this separating chamber. In both of these prior centrifuges, the side of the piston valve facing the separating chamber is entirely exposed to an axial liquid pressure during the periods between the intermittent sludge discharges, this axial pressure acting in the opening direction of the piston valve to effect a sludge discharge and being counteracted by another liquid pressure acting in the closing direction of the piston valve. That surface of the piston valve which is exposed to the closing pressure and contacted by liquid is greater in area and has a greater radius (from the rotor axis) than the surface of the piston valve which is exposed to the opening pressure. If the pressure-generating media acting on opposite sides of the valve have the same specific gravity, the closing pressure will be greater than the opening pressure, and consequently the piston valve will be kept closed while exerting a certain pressure .to effect a sealing against leakage through the sludge outlet. In practice, however, the liquid generating the closing pressure is usually water, whereas the sludge-containing liquid being separated and generating the opening pressure can have a greater specific gravity than the water, due to the sludge content of this liquid. Furthermore, the quantity of sludge accumulating in the sludge chamber during the course of separation causes an increase of the opening pressure. The effect of this is that the closing pressure will not always be sufficient to keep the piston valve closed tightly so as to prevent leakage.

According to the present invention, this leakage in a centrifuge of the type disclosed in the aforementioned German specification is avoided by the provision of means whereby a space partly defined by said radially inner area of the piston valve is maintained free of liquid. Although this space may be maintained free of liquid by means of a discharging device, it is preferable according to the invention to provide means for maintaining this space liquid-tight against admission of liquid from all other spaces within the rotor which are supplied with liquid. By dimensioning the liquid-free space so that it has a sufficiently large radius, it is possible to reduce the opening pressure to such a degree that the closing pressure is strong enough to prevent the aforementioned leakage through the sludge outlet.

The invention is described more in detail below, reference being made to theaccompanying drawing in which FIG. 1 is an axial sectional view of part of an embodiment of the present centrifuge, and FIG. 2 is an enlarged sectional view of a detail shown in FIG. 1.

In FIG. I, a rotor body 1 has a cover 2 which is held fast to the rotor body by a locking ring 3. The rotor is driven by a spindle 4. A stationary inlet pipe 5 for the liquid to be separated opens into a distributor 6. This liquid flows past the lower edge of the distributor 6 into a separation chamber 7, in which a set of conical discs 8 is arranged. In the wall of the rotor body are sludge discharge holes 9, which are opened and closed by an axially movable piston valve 11 guided on the rotor hub 10. In closing position, the valve 11 seals against a ring 12 in the rotor cover 2. Between the underside of the piston valve and the rotor bottom is a space 13 having a draining hole 14 formed in the wall of the rotor body. The piston valve is kept in closed position by supplying operating'liquid, via a hole 15 in the rotor bottom, to the space 13 from a stationary inlet pipe 16 in such a quantity that the space 13 is kept filled with liquid in spite of the drainage through the hole 14. Sludge discharge is effected by interrupting the liquid supply through the pipe 16 and thus causing the liquid quantity in the space 13 to be drained out through the hole 14, so that the piston valve 11 is pressed downward by the liquid pressure prevailing in the separation chamber 7, thereby opening the sludge discharge holes 9. Liquid separated from sludge flows through an interspace 17 between the rotor cover and an upper disc 18 and thence into a paring chamber 19, from which the liquid is pumped out by a paring disc 20.

The piston valve 11 has an upwardly extending cylindrical portion 21 concentric to the rotor axis and which slides along an annular projection 22 on a conical disc 23 fixed to the spindle head 4a. A rubber ring 24 is placed in the annular space formed by the parts 21, 22 and 23-, and this ring seals against leakage of liquid from the separation chamber 7 into a larger annular space 25 between the disc 23 and the hub-like portion 26 of the piston valve.

As shown particularly in FIG. 2, the sealing between the separation chamber 7 and the space 25 is effective in all positions of piston valve 11, which has a firm but sliding contact with the seal ring 24.

i In order to explain the invention, it is first assumed that the details 22 and 24 have been removed from the device as illustrated. The space 25 will then be filled, during a separating operation, with liquid from the separating chamber 7 and which thus generates a downward pressure against the hub-like portion 26 of the piston valve. It can then happen that the pressure of the piston valve against the sealing ring 12 becomes so small that leakage takes place through the holes 9. If now, by means of the parts 22 and 24, the space 25 is liquid-sealed from the separation chamber 7, in the main only atmospheric pressure will prevail in the space 25. This means an appreciable reduction of the opening pressure acting upon the piston valve. In other words, the pressure of the piston valve against the sealing ring 12 is increased correspondingly so as to prevent said leakage, the radial extension of the space 25 being sufficient for this purpose.

As shown in FIG. 1, the side of piston valve 11 which faces the separating chamber 7 includes a first area A, on which the contents of this chamber act to urge valve 11 in the direction for opening the sludge outlet, and further includes a second area'B located radially inward from area A and partly defining a space 25 separated from chamber 7. Also, the conical disc 23 is shown with a first side S1 partly defining the inlet to the separating chamber 7 and with a second side S2 partly defining the space 25.

I claim:

1. In a sludge centrifuge, the combination of a centrifugal rotor mounted for rotation about an axis and having a separating chamber and an inlet for supplying a sludge-containing liquid to said chamber, the rotor also having a separated liquid outlet and a peripheral outlet for separated sludge, an hydraulically operated piston valve movable in the rotor axially thereof to open and close said sludge outlet, said piston valve having one side facing said separating chamber and including a first area on which the contents of said chamber act to urge said valve in the direction to open the sludge outlet, said one side also including a second area located radially inward from said first area and partly defining a space separated from said chamber, and means in the rotor for maintaining said space free of liquid.

2. The combination according to claim 1, in which the rotor has a second chamber for receiving an operating liquid and located on the side of the piston valve opposite said one side facing the separating chamber,

said means including a seal and being operable to separate said space liquid-tight from both of said chambers.

cylindrical surface is slidable.

was UNITED STATES PAT OF (5/69) T I. I CEL'Q'IIFICATE. OF CORRECTION Pai eflt; so, H Dated January Inventor) Klaus Hans Dieter Stroucken It is certified that error appears in the abeve-identified' patent and that said Letters Patent are hereby corrected as shown below:

F I T Column 1, line 11, "N6. 2,041,372"v Should. be

I Column "2, line 39, ."seali should be -sealing- Signed and sealed this 24th day of September; 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. 3 c. MARSHALL DANN Commissioner of Patents Attesting Officer 

1. In a sludge centrifuge, the combination of a centrifugal rotor mounted for rotation about an axis and having a separating chamber And an inlet for supplying a sludge-containing liquid to said chamber, the rotor also having a separated liquid outlet and a peripheral outlet for separated sludge, an hydraulically operated piston valve movable in the rotor axially thereof to open and close said sludge outlet, said piston valve having one side facing said separating chamber and including a first area on which the contents of said chamber act to urge said valve in the direction to open the sludge outlet, said one side also including a second area located radially inward from said first area and partly defining a space separated from said chamber, and means in the rotor for maintaining said space free of liquid.
 2. The combination according to claim 1, in which the rotor has a second chamber for receiving an operating liquid and located on the side of the piston valve opposite said one side facing the separating chamber, said means including a seal and being operable to separate said space liquid-tight from both of said chambers.
 3. The combination according to claim 1, comprising also a conical disc fixed in the rotor and having first and second sides partly defining said inlet and said space, respectively, said one side of the piston valve having a cylindrical surface concentric to the rotor axis, said means including a sealing ring mounted on said second side of the conical disc and on which said cylindrical surface is slidable. 